Alterations in Source-Sink Patterns by Modifications of Source Strength

Abstract

Bean plants, trimed to a simpl"id "double source, doube sink" translocatlon system (the paired primary leaves serving as the double source and the paired lateral laflets of the immature first trifolate leaf as the double sink) were used to study the magnitude and short-term time course of change in the alocatio ratio (parti ratio) of assimilates translocated from the labeled primary leaf to its respective "near" and "far leaflet" sinks in response to an increase or decrease in the source strength of the opposite primary leaf (the "control" leaf). If the rates of net photosynthesis in the two prbiary leaves were similar, assimilates from the labeled source leaf partond to the leaflet sinks in the ratio of 5:1 or higher, the dominant sink beng the leaflet "nearer" to the labeled source leaf. If the rate of net photosynthesis in the control leaf was increased substantially above that of the labeled source leaf, the rate of translocation from the labeled source to either the near leaflet sink or far leaflet sink remained unaffected, despite, presumably, a higber translocation rate from the control leaf, and hence a higher phloem pressure gradient (or increased cross-sectional area) in the transport pathway from the control leaf to the leaflet sinks. If the control leaf was excised, thus reducing the source leaf area by about a half, the translocation rate from the remaining source leaf rapidly doubled, the partition ratio becoming equal to unity. If the control leaf was darkened, the partition ratio adjusted to an intermediate vahle. Athough export rates from the labeled source leaf were increased either by excising or darkening the control leaf, the rate of net photosynthesis in the labeled leaf remained constant.

Sulfur Dioxide Inhibition of Translocation in Bean Plants

“…following treatment period 3, Table II, in Borchers-Zampini et al [2]) failed to increase the partition ratio even though PB rapidly recovered to near its predarkening rate (some recovery has been noted after about 4 h). A possibly related phenomenon is the observation by Borchers-Zampini et al (2) (Fig. 1, left) in response to exposure of leaf B for 2 h to a concentration of 3.0 ,ul/l SO2.…”

“…In the series B experiments, PB was altered by SO2 exposure of B rather than by varying the illuminance of B, as in the experiments by Borchers-Zampini et al (2). The rationale was otherwise similar.…”

“…/P\ /111\ /.,\ double-sink experiments and is closely patterned after recent work by Borchers-Zampini et al (2). Plants selected for this series of experiments were of the same age as were those in the singlesource single-sink experiments, but they were trimmed to the configuration shown in Figure 1 (left).…”

Effect of Translocation-Hindering Procedures on Source Leaf Photosynthesis in Cucumber

“…Borchers-Zampini et al (6) have also demonstrated rapid changes in transport rates from source leaves following sink manipulation. The results reported here thus suggest that decrease in translocation out of source leaves is not directly linked to changes in CO2 assimilation, at least during the first few hours.…”

Effect of Rapid Changes in Sink-Source Ratio on Export and Distribution of Products of Photosynthesis in Leaves of Beta vulgaris L. and Phaseolus vulgaris L.

“…Experimental treatments such as partial shading or defoliation produce rapid changes in patterns and rates of translocation in sink regions (1,4,7). Changes in distribution of '4C-labeled material exported to sink regions monitored with a GM detector are observed to occur within tens of minutes; at this point changes in export may be inferred to occur.…”